There's a video of the supposed autopsy, so you can see an "alien" head.

Personally, I think it's all a load of rubbish. I spent half of my childhood reading about this kind of thing, and if I've taken away anything from that, it's that the authors of conspiracy or paranormal topics heavily embellish the evidence for and disregard the evidence against.

Besides, a number of people have come forward claiming to have engineered the special effects for that video. I think if there was anything, it was the government/air force/whoever doing something naughty so they used aliens to cover it up.